The present invention generally relates to surface micromachined optical systems and, more particularly, to such systems that include at least one structurally reinforced surface micromachined mirror microstructure.
There are a number of microfabrication technologies that have been utilized for making microstructures (e.g., micromechanical devices, microelectromechanical devices) by what may be characterized as micromachining, including LIGA (Lithographie, Galvonoformung, Abformung), SLIGA (sacrificial LIGA), bulk micromachining, surface micromachining, micro electrodischarge machining (EDM), laser micromachining, 3-D stereolithography, and other techniques. Bulk micromachining has been utilized for making relatively simple micromechanical structures. Bulk micromachining generally entails cutting or machining a bulk substrate using an appropriate etchant (e.g., using liquid crystal-plane selective etchants; using deep reactive ion etching techniques). Another micromachining technique that allows for the formation of significantly more complex microstructures is surface micromachining. Surface micromachining generally entails depositing alternate layers of structural material and sacrificial material using an appropriate substrate which functions as the foundation for the resulting microstructure. Various patterning operations may be executed on one or more of these layers before the next layer is deposited so as to define the desired microstructure. After the microstructure has been defined in this general manner, the various sacrificial layers are removed by exposing the microstructure and the various sacrificial layers to one or more etchants. This is commonly called xe2x80x9creleasingxe2x80x9d the microstructure from the substrate, typically to allow at least some degree of relative movement between the microstructure and the substrate. Although the etchant may be biased to the sacrificial material, it may have some effect on the structural material over time as well. Therefore, it is generally desirable to reduce the time required to release the microstructure to reduce the potential for damage to its structure.
Microstructures are getting a significant amount of attention in the field of optical switches. Microstructure-based optical switches include one or more mirror microstructures. Access to the sacrificial material that underlies the support layer that defines a given mirror microstructure is commonly realized by forming a plurality of small etch release holes down through the entire thickness or vertical extent of the mirror microstructure (e.g., vertically extending/disposed etch release holes). The presence of these small holes on the upper surface of the mirror microstructure has an obvious detrimental effect on its optical performance capabilities. Another factor that may have an effect on the optical performance capabilities of such a mirror microstructure is its overall flatness, which may be related to the rigidity of the mirror microstructure. xe2x80x9cFlatnessxe2x80x9d may be defined in relation to a radius of curvature of an upper surface of the mirror microstructure. This upper surface may be generally convex or generally concave. Known surface micromachined mirror microstructures have a radius of curvature of no more than about 0.65 meters.
The present invention is a surface micromachined optical system that is fabricated on a substrate that is compatible with surface micromachining. Multiple structural layers may be utilized by this system. In this regard, the system includes a first mirror microstructure that is movably interconnected with the substrate, and that may be moved relative to the substrate by at least one actuator that is interconnected with the mirror microstructure. Any way of interconnecting the mirror microstructure with the substrate that allows the mirror microstructure to move relative to the substrate in the desired/required manner may be utilized by the present invention. Moreover, any type of actuator, any number of actuators, or both may be utilized to accomplish the desired movement of the mirror microstructure relative to the substrate. All aspects of the present invention that will now be discussed in more detail utilize the various features addressed in this paragraph and will not be repeated on each occasion.
A first aspect of the above-described surface micromachined optical system has a first mirror microstructure that includes a first structural layer that is spaced from the substrate, a second structural layer that is spaced from the first structural layer away from the substrate, and a plurality of first columns that extend between and fixedly interconnect the first and second structural layers (i.e., so that the first and second structural layers are joined together), and further that are appropriately spaced. As such, the first structural layer is disposed between the second structural layer and the substrate, or at a lower elevation or level relative to the substrate than the second structural layer. Relative movement is allowed between the first mirror microstructure associated with the first aspect and the substrate.
Various refinements exist of the features noted in relation to the first aspect of the present invention. Further features may also be incorporated in the first aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. The surface micromachined optical system of the first aspect may include other microstructures at the same or different elevations or levels relative to the substrate than that which is occupied by the first and/or second structural layers and/or the plurality of first columns of the first mirror microstructure of the first aspect. One or more microstructures or a part thereof may also be disposed directly under the first mirror microstructure such that the same is located directly between the first structural layer and the substrate. There will still be a space between the first structural layer and any underlying structure of the system to allow for relative movement between the first mirror microstructure and the substrate.
Typically the first and second structural layers associated with the first aspect will be vertically aligned such that the second structural layer will be directly above the first structural layer, and further such that their respective centers will be vertically aligned. There may be circumstances where such will not be the case. Appropriate materials for the first and second structural layers and the plurality of first columns include polysilicon in which case the substrate may be silicon-based. Other materials that are appropriate for surface micromachining operations may be utilized for the first and second structural layers associated with the first aspect, such as various other forms of silicon; poly germanium-silicon; various metal films (e.g., aluminum); various metals (e.g., Al/Ni); and silicon carbide.
The surface micromachined optical system of the first aspect may be used for various applications, including optical switching, optical correction such as adaptive optics, and optical scanning. Materials that are used to define the second structural layer may possess sufficient optical properties for providing the desired/required optical function. However, it may be desirable to apply an optically reflective layer to the upper surface of the second structural layer to achieve desired optical properties/characteristics for the first mirror microstructure. Appropriate materials that may be deposited on the upper surface of the second structural layer include gold, silver, and aluminum for metal coatings. For metals, gold and an associated adhesion layer are preferable to obtain a suitable reflectance.
Other structural layers may be utilized by the first mirror microstructure of the first aspect. For instance, a third structural layer may be spaced from the second structural layer in a manner such that the second structural layer is located between the first and third structural layers, in which case the third structural layer would provide the desired/required optical functionality. Those features addressed above in relation to the optical features/characteristics of the second structural layer could then be utilized by the third structural layer. Structural interconnection of the third structural layer to the second structural layer may be accomplished by a plurality of second columns that extend between the second and third structural layers to fixedly interconnect the same. In one embodiment, none of the columns that structurally interconnect the first and second structural layers are aligned with any of the columns that structurally interconnect the second and third structural layers.
Increasing the number of spaced, but interconnected structural layers as a general rule and in accordance with the first aspect is believed to increase the rigidity or stiffness of the first mirror microstructure. This may be beneficial for optical as well as other applications. Therefore, a three-layered optical mirror microstructure in accordance with the first aspect should be more rigid or stiffer than a two-layered optical mirror microstructure in accordance with the first aspect. Similarly, a two-layered optical mirror microstructure in accordance with the first aspect should be more rigid or stiffer than a single layer or laminated mirror microstructure.
The first mirror microstructure of the first aspect may also have a desired radius of curvature on its uppermost structural layer. In one embodiment, the radius of curvature of a structurally reinforced structural layer in the first mirror microstructure that provides an optical function in accordance with the first aspect is at least about 1 meter, in another embodiment is at least about 2 meters, and in yet another embodiment is about 14 meters.
A second aspect of the above-described surface micromachined optical system has a mirror microstructure that includes a first structural layer that is spaced from the substrate, a second structural layer that is spaced from the first structural layer away from the substrate, and a plurality of at least generally laterally extending first ribs or rails that also extend between and structurally interconnect the first and second structural layers so as to fix the first structural layer to the second structural layer. Ribs or rails differ from columns in that the ribs or rails have a length dimension that is greater (and typically significantly greater) than their width dimension, in contrast to the types of columns addressed above in relation to the first aspect which do not. As in the case of the first aspect, the first structural layer is disposed between the second structural layer and the substrate, or at a lower elevation or level relative to the substrate than the second structural layer. Relative movement is also allowed between the first mirror microstructure associated with the second aspect and the substrate.
Various refinements exist of the features noted in relation to the second aspect of the present invention. Further features may also be incorporated in the second aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. The surface micromachined optical system of the second aspect may include other microstructures at the same or different elevations or levels relative to the substrate than that which is occupied by the first and/or second structural layers and/or the plurality of first rails of the first mirror microstructure of the second aspect. One or more microstructures or a part thereof may also be disposed directly under the first mirror microstructure such that the same is located directly between the first structural layer and the substrate. There will still be a space between the first structural layer and any underlying structure of the system to allow for relative movement between the first mirror microstructure and the substrate.
Typically the first and second structural layers associated with the second aspect will be vertically aligned such that the second structural layer will be directly above the first structural layer, and further such that their respective centers will be vertically aligned. There may be circumstances where such will not be the case. Appropriate materials for the first and second structural layers, as well as the plurality of first rails, include polysilicon in which case the substrate may be silicon-based. Other materials that are appropriate for surface micromachining operations may be utilized by the second aspect as well and as noted above in relation to the first aspect.
The surface micromachined optical system of the second aspect may then be used for the type of optical applications addressed above in relation to the first aspect. Materials that are used to define the second structural layer may possess sufficient optical properties/characteristics for providing the desired/required optical function. However, it may be desirable to apply an optically reflective layer to the upper surface of the second structural layer to achieve desired optical properties/characteristics for the first mirror microstructure, including those noted above in relation to the first aspect.
As noted above, the plurality of first rails associated with the second aspect are at least generally laterally extending. xe2x80x9cAt least generally laterally extendingxe2x80x9d herein, and specifically in the context of the second aspect, means that the plurality of first rails extend at least generally parallel with the substrate. Typically this will be such that the first rails will be disposed at a constant, fixed elevation relative to the first substrate, although such may not necessarily be the case (i.e., the elevation of one or more of the first rails relative to the substrate may change progressing along its length). Various layouts of the plurality of first rails may be utilized. For instance, the plurality of first rails may be disposed: 1) in at least substantially parallel relation; 2) in non-intersecting relation; 3) so as to extend at least toward (and thereby including to) a first point (e.g., each of the first rails may terminate at least substantially equidistantly from this first point; one or more of the first rails may extend closer to the first point than at least one other first rail; at least two of the first rails may intersect at the first point; or any combination thereof); 4) such that at least two of the first rails extend at least toward (and thereby including to) a first point, and such that at least two other first rails extend at least toward (and thereby including to) a second point that is spaced from the first point (i.e., not all first rails need to converge toward the same common point); 5) such that at least two of the first rails intersect; and 6) any combination thereof. Yet another embodiment has multiple groups of the first rails that are in different orientations. For instance, one group of the first rails may all extend in a first direction, and another group of the first rails may all extend in a second direction that is different from the first direction, and including being perpendicular to the first direction to define a waffle-like pattern. Stated another way, the structural interconnection between the first and second structural layers may be in the form of a grid or the like, and the first rails associated with the second aspect may be considered as a part thereof.
Multiple configurations may define the length dimension of the first rails or how the extend within the lateral dimension. For instance, the first rails may be axially or linearly extending in the lateral dimension (i.e., the first rails may extend laterally in axial or linear fashion). The first rails may also extend in non-linear fashion in the lateral dimension as well. One example is where the first rails meander in the lateral dimension, such as sinusoidally or in a xe2x80x9czig-zagxe2x80x9d fashion within a plane that is at least generally parallel relation with the substrate.
Other structural layers may be utilized by the first mirror microstructure of the second aspect. For instance, a third structural layer may be spaced from the second structural layer in a manner such that the second structural layer is located between the first and third structural layers, in which case the third structural layer would provide the desired/required optical functionality. Those features addressed above in relation to the optical features/characteristics of the second structural layer could then be utilized by the third structural layer. Structural interconnection of the third structural layer to the second structural layer may be accomplished by a plurality of at least generally laterally extending second ribs or rails that extend between and structurally interconnect the second and third structural layers so as to fix the third structural layer to the second structural layer. The various characteristics/features discussed above in relation to the plurality of first rails are equally applicable to the plurality of second rails. In one embodiment, the plurality of first rails are disposed in a first orientation in the lateral dimension and the plurality of second rails are disposed in a second, different orientation in the lateral dimension. These first and second orientations may be such that the plurality of first rails are disposed in an at least substantially perpendicular orientation to the plurality of second rails.
Increasing the number of spaced, but interconnected layers as a general rule and in accordance with the second aspect is believed to increase the rigidity or stiffness of the first mirror microstructure, which is beneficial in optical applications. Therefore, a three-layered optical mirror microstructure in accordance with the second aspect should be more rigid or stiffer than a two-layered optical mirror microstructure in accordance with the second aspect. Similarly, a two-layered optical mirror microstructure in accordance with the second aspect should be more rigid or stiffer than a single layer or laminated mirror microstructure.
The microstructure of the second aspect may also have a desired radius of curvature on its uppermost structural layer. In one embodiment, the radius of curvature of a structurally reinforced structural layer in the first mirror microstructure in accordance with the second aspect is at least about 1 meter, in another embodiment is at least about 2 meters, and in yet another embodiment is about 14 meters.
A third aspect of the above-described surface micromachined optical system has a mirror microstructure that includes a first structural layer that is spaced from the substrate, a second structural layer that is spaced from the first structural layer away from the substrate, and at least one structural interconnection that extends between and fixedly interconnects the first and second structural layers. An upper surface of the second structural layer has a radius of curvature that is at least about 1 meter, and more typically at least about 2 meters. Therefore, the upper surface of the second structural layer is substantially flat which makes the first mirror microstructure of this third aspect particularly beneficial for various optical applications. The various features discussed above in relation to the first and second aspects may be utilized by this third aspect of the present invention as well, alone or in any combination.
A fourth aspect of the above-described surface micromachined optical system has a mirror microstructure that includes a first structural layer that is spaced from the substrate, and at least one structurally reinforcing member that extends from the first structural layer toward, but not to, the substrate. Each such structural reinforcement member may fixedly attach to an underlying structural layer, although such need not be the case (i.e., the structural reinforcement member(s) of the fourth aspect may be cantilever, or may be of the form of the first mirror microstructures noted above in relation to the first or second aspects). The first structural layer has an upper surface with a radius of curvature that is at least about 1 meter, and more typically at least about 2 meters. Therefore, the upper surface of the first structural layer is substantially flat which makes the first mirror microstructure of this fourth aspect particularly beneficial for use in various optical applications. The various features discussed above in relation to the first and second aspects may be utilized by this fourth aspect of the present invention as well, alone or in any combination.
A fifth aspect of the above-described surface micromachined optical system has a mirror microstructure that includes a first structural layer that is spaced from the substrate, a second structural layer that is spaced from the first structural layer away from the substrate, and at least one structural interconnection that extends between and fixedly interconnects the first and second structural layers. A first structural interconnection that fixes the first structural layer to the second structural layer is positioned to provide a reinforcement ratio of no more than about 0.5. This reinforcement ratio is a ratio of a first distance to a second distance. The first distance is a distance from a center of the second structural layer in the lateral dimension to a portion of the first structural interconnection that is disposed closest to the center of the second structural layer. The second distance is the diameter of the second structural layer. Therefore, the second structural layer is structurally reinforced at least close to (and thereby including at) its center.
A sixth aspect of the above-described surface micromachined optical system has a mirror microstructure that includes a first structural layer that is spaced from the substrate, and at least one structural reinforcing member that extends from the first structural layer toward, but not to, the substrate. Each structural reinforcement member may fixedly attached to an underlying structural layer, although such need not be the case (i.e., the structural reinforcement member(s) of the sixth aspect may be cantilever, or may be of the form of the structures noted above in relation to the first or second aspects). A first structural reinforcement member that extends down from the first structural layer is positioned to provide a reinforcement ratio of no more than about 0.5. This reinforcement ratio is a ratio of a first distance to a second distance. The first distance is a distance from a center of the second structural layer in the lateral dimension to a portion of the first structural reinforcement member that is disposed closest to the center of the second structural layer. The second distance is the diameter of the second structural layer. Therefore, the second structural layer is structurally reinforced at least close to (and thereby including at) its center.
A seventh aspect of the above-described surface micromachined optical system has a mirror microstructure that includes a first structural layer that is spaced from the substrate, a second structural layer that is spaced from the first structural layer away from the substrate, at least one structural interconnection that extends between and fixedly interconnects the first and second structural layers, a third structural layer that is spaced from the second structural layer away from the second structural layer, and at least one structural interconnection that extends between and fixedly interconnects the second and third structural layers. The various features discussed above in relation to the first and second aspects may be used by this seventh aspect as well, alone or in any combination, including using the various reinforcing structures noted above for the structural interconnections between the first and second structural layers, and between the second and third structural layers.